The present invention relates to an electronic electric power meter, and more particularly to the simulation of the rotation of a power meter disk which is present in conventional electro-mechanical power meters, but which is not present in electronic power meters.
In a conventional electro-mechanical power meter, an eddy current disk is caused to rotate at a rate proportional to the power being consumed by the load being metered. Meter technicians at the factory and in the field use the rotation of the meter disk on such conventional electro-mechanical watt hour meters for timing measurements during various meter tests. Since the power meter is conventionally enclosed within a glass or plastic transparent cover, the rotation of the eddy current meter disk can be readily viewed even in an assembled power meter. A timing mark or line is conventionally provided on the outer edge of the meter disk such that it is visible at any given location exactly once per revolution of the metered disk. By counting the number of times that the timing mark or line is observed at a given location as the disk revolves for a given period of time, the number of kilowatt hour pulses that should have been accumulated by the register, which accumulates and displays power consumption, can be determined.
With the use of microprocessors in certain new designs of electronic electric power meters, pulses are derived electronically and displayed, for example, on a liquid crystal alpha-numeric display such that a rotating disk is not necessary, and is not included, in such designs. An example of an electronic power meter is described in U.S. Pat. No. 5,001,420, issued Mar. 19, 1991 by W. R. Germer, M. J. Ouellette, D. F. Bullock, and A. F. Palmer, entitled Modular Construction for Electronic Energy Meter, assigned to the same assignee as the present invention, and hereby incorporated by reference.
With such electronic power meters, an alternate method of timing must be provided for the various tests that have previously been conducted utilizing the timing mark on the meter disk. However, it is desirable that an alternate meter disk timing method for an electronic power meter not require any hardware beyond that required and provided by the existing alpha-numeric display on the register of the power meter. In addition, it is highly desirable that the alternate meter disk timing method be as easy to use for a meter technician as possible, be as accurate as the original meter disk timing method, and impose a minimum burden, or loading, on the timing and space limitations of the software used in electronic power meters. Since the meter technician is trained and familiar with the use of a moving timing mark it is highly desirable to have the alternate timing arrangement provide a simulated meter disk rotation which visually appears as close as possible to that provided by the timing mark in an electro-mechanical power meter.
The desirability of simulating the meter disk in an electronic liquid crystal display (LCD) has been addressed but not satisfactorily solved. U.S. Pat. No. 4,902,964 issued Feb. 20, 1990, describes the provision of a "caterpillar crawl" LCD segment array controlled by a microprocessor to correspond to the rotation of the rotating shuttered disk of an optical pulse initiator. The array is included in an electronic demand register in which the segments are sequentially illuminated in groups of three segments to correspond to the rotation of the shuttered disk, and in which the display is hi-directional to accommodate forward and reverse rotations of the shuttered disk. Such an arrangement requires the provision of an optical shutter disk, but more importantly requires a special "caterpillar crawl" segment array or display in the liquid crystal display. This requires a special display in addition to the normal segmented display which is selectively energized to provide alpha-numeric display characters. Such an arrangement requires special manufacturing masks for the LCD, and a special LCD display element to accommodate the "caterpillar crawl" segment array. This adds complexity and cost to the power meter. U.S. Pat. No. 4,686,460 issued Aug. 11, 1987 provides a vector whose direction indicates the direction of flow of power on the lines measured and whose length approximates the magnitude. Different signals are selected for different speeds of rotation. Such prior arrangements have not proven entirely satisfactory for the reasons indicated above and as discussed below.
It is an object of the present invention to provide an electric power meter eddy current disk rotation simulator which is familiar in appearance, and is easy to use by a meter technician.
It is another object of the present invention to provide an electric power meter eddy current disk rotation simulator which is accurate, yet imposes a minimum burden on the timing and space limitations of the software in an electronic power meter.
It is still another object of the present invention to provide an eddy current disk rotation simulator in an electronic electric power meter which uses existing alpha-numeric symbol displays without the necessity of special displays or special display manufacturing requirements.
It is a further object of the present invention to provide an eddy current disk rotation simulator in an electronic power meter which visually approximates the spinning eddy current disk of an electro-mechanical induction power meter.
It is a still further object of the present invention to provide an electric power meter eddy current disk rotation simulator which visually displays direction of rotation and energy flow.
In accordance with one embodiment of the present invention, the rotation of the eddy current disk in a conventional electro-mechanical power meter is simulated in an electronic power meter which does not include a meter disk but which includes a plurality of segmented characters for displaying power. Power consumption is displayed on the segmented characters with a time sharing arrangement to display the simulated meter disk rotation upon interruption of the display of power consumption. Horizontal display segments are produced in the center of the segmented characters, extending beyond a single segmented character, and are generated in response to pulses of the electronic power meter which vary in accordance with power consumption by the load. The horizontal display segments are caused to move across the segmented characters in response to a command signal, and to disappear in part at one end of the segmented characters while at the same time appearing at the opposite side.
The top and bottom of the horizontal segments of the segmented characters are energized to provide parallel lines during the simulation in order to simulate the gap in which the conventional electro-mechanical meter disk rotates. There are 6 segmented characters, each of which have a center of 2 segments, and 12 states are applied to correspond to the 12 pulses per revolution in a conventional power meter. The direction of movement is made responsive to the direction of energy flow relative to the load. The number of times the horizontal display segments return to the same position may be counted over a period of time to enable testing of the operation of the electronic power meter in the same manner a timing mark on the meter disk in a conventional power meter is used for counting and timing purposes.